1. Field of the Invention
The present disclosure relates to a novel copolymer, an organic solar cell comprising the same and a method for fabricating the organic solar cell.
2. Description of the Prior Art
Since the possibility of solar cells based on organic copolymers was first shown by Heeger at the University of California, Santa Barbara (UCSB), in 1992, there have been many studies thereon. Such solar cells include heterojunction thin film devices comprising a mixture of an organic copolymer, which absorbs light, with a C60 or C70 fullerene derivative which has a very high electron affinity. These heterojunction thin film devices comprise a transparent positive electrode made of indium tin oxide (ITO) and a negative electrode made of a metal such as Al, which has a low work function.
In such solar cells, the photoactive layer comprising the organic copolymer absorbs light to form electron-hole pairs or excitons. The electron-hole pairs move to the interface between the copolymer and the C60 or C70 fullerene derivative at which they are separated into electrons and holes. Then, the electrons move to the metal electrode, and the holes move to the transparent electrode, thereby generating electrodes.
Currently, the efficiency of organic copolymer thin-film solar cells based on organic copolymers reaches 7-8% (Nature Photonics, 2009, 3, 649-653).
However, the efficiency of the organic copolymer solar cell is still low compared to the maximum efficiency of solar cells based on silicon (about 39%). Thus, the development of organic polymer solar cells having a higher efficiency is required.
Korean Patent Laid-Open Publication No. 10-2010-0111767 discloses a conductive copolymer comprising 2,7-carbazole in the main chain, and an organic solar cell comprising the same. According to the disclosure of the above patent publication, the conductive copolymer comprising 2,7-carbazole in the main chain improves light absorption and hole mobility to improve the efficiency of the solar cell.
However, there is a problem in that it is not easy to improve optical efficiency, because the mobility of holes is relatively lower than the mobility of electrons, despite the use of 2,7-carbazole.